TRENTON — U.S. Rep. Rush Holt Jr. had just finished giving a speech to environmentalists in Washington about 10 years ago when a stranger approached him.

"He came up to me and said: ‘You’re Rush Holt? I’ve been wanting to meet you,’ " Holt said. "He said: ‘My middle name is Rush. I’m named for your father.’ "

Holt (D-12th Dist.) did not know his father, Rush Holt Sr., for long. The elder Holt — an eccentric lifelong politician whose career peaked with a single term as a U.S. senator from West Virginia — died of cancer when his son was 6.

But throughout his life, Holt, 64, has learned about his namesake through people his father influenced decades ago — as well as their kids. The man who told Holt he was named after his father said it was because his own dad was a coal miner and "to his dying day said a coal miner never had a better friend than Rush Holt."

Now, Holt hopes to join the Senate himself, almost 73 years after his father left the office. He’s running as an underdog in the four-way Aug. 13 Democratic primary to succeed the late Sen. Frank Lautenberg (D-N.J.). The field includes Newark Mayor Cory Booker, the camera-friendly front-runner.

"Ultimately, people want a workhorse, not a show horse," Holt said of the race. "I’m not going to elaborate on that statement. Take it for what it’s worth."

Congressman Rush Holt campaigns for SenateNew Jersey Congressman Rush Holt campaigns for the late Frank Lautenberg's seat in the US Senate at the Plainfield July Fourth parade on Saturday, July 7, 2013. (Frances Micklow / The Star-Ledger)

Holt’s career is a very different story from his father’s, who was voted out of office almost eight years before his son was born.

While Holt Sr. was a firebrand, Holt Jr. has developed a reputation as a quiet but effective policy wonk. Holt Sr. alienated his political allies. Holt Jr. steadily built relationships.

"Rush is a respecter of institutions. He’s a diligent guy. He’s not a bomb thrower," said Ross K. Baker, a political science professor at Rutgers who studies Congress. "He followed the kind of traditional playbook for members of Congress."

Holt Sr., the son of a small-town mayor in West Virginia, was elected to the U.S. Senate at age 29 — to this day, the youngest senator ever popularly elected. In fact, the "Boy Senator" had to wait six months to take office because he hadn’t reached the constitutionally required age of 30.

In a house that prized seniority, Holt Sr. refused to keep a low profile, once filibustering a bill because he felt it didn’t give enough help to coal workers, running as a Franklin Roosevelt Democrat but criticizing the New Deal and staking out stances to the left of the liberal president. And as the country headed toward World War II, Holt Sr. protested.

"Obviously, I never learned practical politics from him. And besides, he was such an independent-minded person, I’m not sure you would want to learn practical politics from him," Holt said, adding he’s certain he wouldn’t have agreed with his father’s position on the war.

Sen. Rush Holt, Sr. is shown in this photo, taken in either 1938 or 1939. Library of Congress

"But I really did learn an awful lot from him," he added. "I would run into people — complete strangers — who would hear my name and somehow know who I was, and tell me how much my father meant to them, or how much he helped them. It’s pretty powerful for a little kid to be walking down the street and hear that."

Holt said he was also inspired by his mother, Helen, who turns 100 next month. A scientist and teacher, she was West Virginia’s first female secretary of state. "She never thought of herself as a trailblazer, but she really was in a lot of ways," he said.

PATH TO POLITICS

For most of his life, Holt’s career more resembled his mother’s.

He didn’t run for office until he was nearly 50. Instead, he served in academia, getting a doctorate in physics and teaching at Swarthmore College, then working as a research scientist at Princeton. His résumé also includes a stint as acting chief of the Office of Strategic Forces Analysis at the Department of State’s Nuclear and Scientific Division.

He settled in New Jersey in 1989 and first ran for Congress seven years later, finishing third in the Democratic primary.

NEW JERSEY'S SPECIAL U.S. SENATE RACE

Two years after that, Holt, an underdog, unseated freshman Republican Mike Pappas, who had sung on the House floor a politically devastating rendition of "Twinkle, Twinkle Kenneth Starr," in praise of the independent counsel whose report was the basis of President Clinton’s impeachment.

"I knew I had him when I heard him on the news that day," Holt said, jokingly. "Of course that’s not true. I’m not that cocky."

The soft-spoken, studious Holt — known for beating IBM supercomputer "Watson" in a mock round of "Jeopardy!" — has never been a headline grabber in representing his Central Jersey district. His speeches are heavier on policy than rhetoric, and he gently pokes fun at Booker’s celebrity while portraying himself as a get-down-to-business political veteran.

Holt — whose wife, Margaret Lancefield, is a physician in Princeton — is also burnishing his reliably liberal congressional record, reminding voters of his votes against the Iraq war and extending the Patriot Act, and his attempts to curb global warming.

Holt said that if elected to the Senate, he would focus on boosting education and scientific research, and protecting civil rights and liberties. And he would continue to push for universal health care coverage through a single-payer system — something liberals have long pushed for, but was not part of the proposals that became the Affordable Care Act.

"There’s no question that the Affordable Care Act, which is a huge improvement for health care in America, is kind of cobbled together by compromise in a way that is not most efficient and most beneficial to people," Holt said. "I think we will before long come to the conclusion that it’s time to move to universal, single-payer coverage."

To accomplish such goals, Holt said his role model would be Hillary Clinton.

"She sat down with Sen. (Robert) Byrd," he said, mentioning the conservative West Virginia Democrat.

"A lot of people said, ‘He’s not a progressive like you are.’ And she said ‘I want to learn.’ And everybody credits her with being a very effective senator because she went about the job in the right way," Holt said. "It wasn’t about grandstanding. It was about working."